1. Field of the Invention
This invention relates to a method of producing very thin films of magnetic material and to the material.
2. Brief Description of the Prior Art
Very thin films with layers of magnetic material have been known in the prior art. A dissertation of Rodger Michael Walser entitled A Study of Thin Film Magnetodielectrics, 1967, University of Michigan, discloses a material consisting of several stacked layers of alternating thin magnetic or ferrite material films surrounded by dielectric material wherein the magnetic material films are each less than skin depth (about 0.3 microns) because of the need to limit the thickness of each layer to less than an electromagnetic skin depth at the frequency of use. The "skin depth" is the distance below the surface of an electrical conductor in which current will flow at the frequency of operation, this being a well known phenomenon.
The material described by Walser, known for its high complex dielectric and magnetic susceptibility at frequencies above and below 1 GHz. The processes required to fabricate this material include thin film vapor deposition and photolithography or micromasking repeated many times to produce an appreciable thickness for practical use. The cost of commercial manufacture and application of this material, which provides an ultra thin magnetic absorber, is very high, therefore severely limiting its use to very few applications having small areas of concern and a high dollar value. The above described film as well as the low cost magnetodielectric material of this invention has utility in at least the following areas: size reduction of inductors on electronic integrated circuit chips and miniaturization of electronic circuits, electromagnetic interference (EMI) reduction in electronic packages, modules and housings, RF multipath reduction from buildings or towers and size reduction and/or performance improvement of UHF, VHF and microwave antennas.
Iron carbonyl powder in a plastic or rubber and ceramic such as hexagonal ferrites have been used in the above applicatons. Both of these types of materials have a high specific gravity (as high as 5 in iron carbonyl powder in plastic) and have relatively low values of magnetic susceptance, requiring thickness and weights that are an order of magnitude greater to accomplish the same effects and tasks.
It is therefore apparent that there is a substantial need for a low cost form of a material of the type described by Walser. To date, no such material is known which has relatively low cost.